Structural color of metallic glass through picosecond laser

The alteration in surface color of metallic glasses(MGs)holds great significance in the context of microstructuredesign and commercial utility.It is essential to accurately describe the structures that are formed during the laser and colorseparation processes in order to develop practical laser coloring applications.Due to the high oxidation sensitivity of Labasedmetallic glass,it can broaden the color range but make it more complex.Structure coloring by laser processing on thesurface of La-based metallic glass can be conducted after thermoplastic forming.It is particularly important to clarify therole of structure and composition in the surface coloring process.The aim is to study the relationship between amorphoussurface structural color,surface geometry,and oxide formation by laser processing in metallic glasses.The findings revealedthat the periodic structure primarily determines the surface color at laser energy densities below 1.0 J/mm^(2).In contrast,thesurface color predominantly depends on the proportion of oxides that are formed when energy densities exceed 1.0 J/mm^(2).Consequently,this study provides a novel concept for the fundamental investigation of laser coloring and establishes a newavenue for practical application.

Ultra-soft Desorption Assisted Mass Spectrometry using Picosecond Infrared Laser for the Detection of lons in the Liquid Surface

To identify the species in liquid surface using mass spectrometry,we must eliminate or reduce interferences during the vaporization or desorption of the species from the liquid surface.It is much more challenging to isolate the ionic,larger species from the liquid surface,because of the frangible structures and the higher solvation energies of those species.Here we demonstrate a new mass spectrometry in which the ionic species at the liquid surface can be desorbed with ultrasoft infrared picosecond laser pulses while the liquid surface is not breached.This laser desorption assisted mass spectrometry is not only a powerful tool to detect the fragile species but also promising to investigate vibrational energy transfer dynamics in the liquid surface.

Proton acceleration from picosecond-laser interaction with a hydrocarbon target

As an intense picosecond laser pulse irradiates a hydrocarbon target,the protons therein can be accelerated by the radiation pressure as well as the sheath field behind the target.We investigate the effect of the laser and hydrocarbon target parameters on proton acceleration with two/threedimensional particle-in-cell simulations.It is found that the resulting two-ion species plasma can generate a multiple peaked charge-separation field that accelerates the protons.In particular,a smaller carbon-to-hydrogen ratio,as well as the thinner and/or lower density of the target,leads to a larger sheath field and thus proton beams with a larger cutoff energy and smoother energy spectrum.These results may be useful in achieving high-flux quasi-monoenergetic proton beams by properly designing the hydrocarbon target.

A Comparison in Laser Precision Drilling of Stainless Steel 304 with Nanosecond and Picosecond Laser Pulses

Precision drilling with picosecond laser has been advocated to significantly improve the quality of micro-holes with reduced recast layer thickness and almost no heat affected zone.However,a detailed comparison between nanosecond and picosecond laser drilling techniques has rarely been reported in previous research.In the present study,a series of micro-holes are manufactured on stainless steel 304 using a nanosecond and a picosecond laser drilling system,respectively.The quality of the micro-holes,e.g.,recast layer,micro-crack,circularity,and conicity,etc,is evaluated by employing an optical microscope,an optical interferometer,and a scanning electron microscope.Additionally,the micro-structure of the samples between the edges of the micro-holes and the parent material is compared following etching treatment.The researching results show that a great amount of spattering material accumulated at the entrance ends of the nanosecond laser drilled micro-holes.The formation of a recast layer with a thickness of;5μm is detected on the side walls,associated with initiation of micro-cracks.Tapering phenomenon is also observed and the circularity of the micro-holes is rather poor.With regard to the micro-holes drilled by picosecond laser,the entrance ends,the exit ends,and the side walls are quite smooth without accumulation of spattering material,formation of recast layer and micro-cracks.The circularity of the micro-holes is fairly good without observation of tapering phenomenon.Furthermore,there is no obvious difference as for the micro-structure between the edges of the micro-holes and the parent material.This study proposes a picosecond laser helical drilling technique which can be used for effective manufacturing of high quality micro-holes.

Picosecond Laser Surface Texturing of a Stavax Steel Substrate for Wettability Control

In this investigation,a picosecond laser was employed to fabricate surface textures on a Stavax steel substrate,which is a key material for mold fabrication in the manufacturing of various polymer products.Three main types of surface textures were fabricated on a Stavax steel substrate:periodic ripples,a two-scale hierarchical two-dimensional array of micro-bumps,and a micro-pits array with nanoripples.The wettability of the laser-textured Stavax steel surface was converted from its original hydrophilicity into hydrophobicity and even super-hydrophobicity after exposure to air.The results clearly show that this super-hydrophobicity is mainly due to the surface textures.The ultrafast laserinduced catalytic effect may play a secondary role in modifying the surface chemistry so as to lower the surface energy.The laser-induced surface textures on the metal mold substrates were then replicated onto polypropylene substrates via the polymer injection molding process.The surface wettability of the molded polypropylene was found to be changed from the original hydrophilicity to superhydrophobicity.This developed process holds the potential to improve the performance of fabricated plastic products in terms of wettability control and easy cleaning.

Picosecond terahertz pump-probe realized from Chinese terahertz free-electron laser

Electron energy relaxation timeτis one of the key physical parameters for electronic materials.In this study,we develop a new technique to measureτin a semiconductor via monochrome picosecond(ps)terahertz(THz)pump and probe experiment.The special THz pulse structure of Chinese THz free-electron laser(CTFEL)is utilized to realize such a technique,which can be applied to the investigation into THz dynamics of electronic and optoelectronic materials and devices.We measure the THz dynamical electronic properties of high-mobility n-GaSb wafer at 1.2 THz,1.6 THz,and 2.4 THz at room temperature and in free space.The obtained electron energy relaxation time for n-GaSb is in line with that measured via,e.g.,four-wave mixing techniques.The major advantages of monochrome ps THz pump-probe in the study of electronic and optoelectronic materials are discussed in comparison with other ultrafast optoelectronic techniques.This work is relevant to the application of pulsed THz free-electron lasers and also to the development of advanced ultrafast measurement technique for the investigation of dynamical properties of electronic and optoelectronic materials.

Ionization behavior and dynamics of picosecond laser filamentation in sapphire

Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamentation and analyzed the ionization dynamics of the filamentation.Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material.The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track.By increasing laser energy,the length of the damage and filamentary track appeared to increase.In addition,the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations,but no increase in the filamentary zone diameter was observed with increasing laser energy.

Picosecond Laser Machining of Deep Holes in Silicon Infiltrated Silicon Carbide Ceramics

Silicon infiltrated silicon carbide （Si-SiC） ceramics, as high hardness materials, are difficult to machine, especially drilling micro-holes. In this study, the interaction of picosecond laser pulses （1 ps at 1 030 nm） with Si-SiC ceramics was investigated. Variations of the diameter and depth of circular holes with the growth of the laser energy density were obtained. The results indicate that the increase of machining depth follows a nonlinear relation with the increasing of laser energy density, while the diameter has little change with that. Moreover, it is found that some debris and particles are deposited around and inside the holes and waviness is in the entrance and at walls of the holes after laser processing.

Spatiotemporal evolution of high-aspect-ratio filamentary trace in sapphire of picosecond pulse burst-mode for laser lift-off

The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasma string induced by sub-pulses of the burst-mode is revealed according to the analysis of the instantaneous photoluminescence images. Due to the presence of residual plasma, the energy loss of sub-pulse during the balancing of self-focusing effect is reduced, and thus refreshes the plasma via refocusing. The refreshed plasma peak generated by the subsequent subpulse appears at relatively low density positions in the formed filamentary plasma string, which results in more uniform densities and less spatial overlap among the plasma peaks. The continuity and uniformity of the filamentary trace in sapphire are enhanced by the burst-mode. Besides, the burst filamentary propagation can also remain effective when the sub-pulse energy is below the self-focusing threshold. Based on this uniform and precise energy propagation mode, the feasibility of its use for the laser lift-off(LLO) process is verified.

Bioinspired superwetting surfaces for fog harvesting fabricated by picosecond laser direct ablation

Fog harvesting has been considered as a promising method for solving water crisis in underdeveloped regions.To mimic and optimize the alleged natural fog harvesting ability of the stenocara beetle,hybrid superhydrophobic(hydrophobic,superhydrophilic)/hydrophilic patterns are processed on stainless steel via picosecond laser direct writing.Basically,after laser processing,the surfaces of stainless steel change from hydrophilic to superhydrophilic.Then,after chemical and heat treatment,the superhydrophilic surfaces become superhydrophobic with ultra-low adhesion,and superhydrophobic(hydrophobic)with ultra-high adhesion,respectively.This work systematically examines the fog harvesting ability of picosecond laser treated surfaces(LTS),pristine surfaces(PS),laser and chemical treated surfaces(LCTS),laser and heat-treated surfaces(LHTS).Compared with the PS,the as-prepared surfaces enhanced the fog harvesting efficiency by 50%.This work provides a fast and simple method to fog collectors,which offer a great opportunity to develop water harvesters for real world applications.

Effect of thermally induced birefringence on high power picosecond azimuthal polarization Nd:YAG laser system

Pulse-burst 1064-nm picosecond azimuthal polarization beam amplification up to an average power of 16.32 W using side-pumped Nd: YAG amplifiers has been demonstrated. The maximum envelop energy as much as 16.32 mJ, corresponding to a power amplification factor of 299.5%. A simple criterion was defined to help estimate the amount of depolarization in Nd:YAG amplifier stages. The degree of depolarization of the beam was 7.1% and the beam quality was measured to be M2= 3.69. The reason for the azimuthal polarization depolarization and beam quality degradation were explained theoretically and experimentally during the amplification process.

Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO_3 optical parametric amplifiers

Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO：LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 脳 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.

Kinetics study of the solvated electron decay in THF using laser-synchronised picosecond electron pulse

Picosecond pulse radiolysis of neat tetrahydrofuran (THF) shows a fast decay of the solvated electron within 2.5ns.The decay of the solvated electron observed at 790nm is because of spur reaction.A numerical simulation using time dependent Smoluchowski equation containing a sink term with a distance dependent reaction rate is used to fit the pulse-probe data and shows that the geminate reaction can proceed at long distance in this low polar solvent.

皮秒/纳秒脉冲激光抛光对激光选区熔化TC4表面完整性影响

以激光选区熔化TC4钛合金薄壁结构件为研究对象,采用皮秒脉冲激光和纳秒脉冲激光进行激光抛光,旨在探究不同激光抛光方式对增材制造的钛合金表面性能的影响。两种激光加工参数均为优化后的工艺参数,且均为高斯光源。对抛光后的表面形貌、表面粗糙度、热影响层深度、元素分布、氧化程度和试样的拉伸性能进行对比分析。结果表明皮秒脉冲激光和纳秒脉冲激光均可以显著改善增材制造TC4钛合金的表面质量,降低表面粗糙度,从原始的3.52μm下降至皮秒抛光的0.71μm或纳秒激光的0.66μm。纳秒脉冲激光具有更高的热积累,表面氧化程度高,热影响层深,约为34.20μm,比皮秒脉冲激光热影响层深度增大约40.9%。拉伸试验结果表明,虽然激光抛光略微降低了激光选区熔化增材制造钛合金的拉伸性能,但是纳秒脉冲激光抛光后试样的拉伸强度和拉伸应变下降更显著。本研究为激光抛光在增材制造中的应用提供了深入的试验分析和理论探讨,为进一步扩展皮秒脉冲激光在高性能金属零件的制备提供了新思路和方法。

基于响应面法的Ni60/WC涂层表面织构皮秒分束工艺参数预测研究

目的实现六分束激光在Ni60/WC涂层表面烧蚀目标织构激光加工工艺参数的精确选择。方法基于CCD响应面法,设计在不同的激光工艺参数下对Ni60/WC涂层表面进行织构烧蚀试验,以激光频率、扫描次数、扫描速度为影响因素,以圆凹坑织构直径、深度及由其直径和深度综合加权所得的综合目标为响应目标,建立目标织构所需激光工艺参数的预测模型,以织构直径、深度及综合目标作为优化条件,对预测模型进行实验验证。结果扫描次数对织构直径的影响最显著,单个脉冲光斑上所聚集的能量大小是影响织构直径误差的关键因素。对织构深度影响最显著为扫描次数和频率,织构深度与扫描次数、频率呈正相关,不同因素间的交互作用是影响织构加工结果的关键。通过对预测模型所优选的参数进行实验验证发现,以织构直径和深度、综合目标建立的预测模型优选工艺参数所加工圆凹坑织构的质量评价指标与其预测指标的误差率分别为19.37%、3.57%。功率为6 W时,六分束激光加工最优工艺参数为速度5500 mm/s、频率400 kHz、扫描2次。结论通过综合目标建立的Ni60/WC涂层表面圆凹坑织构六分束激光加工参数优选预测模型精确程度较高,能够实现Ni60/WC涂层表面加工所需织构激光参数的准确预测,为涂层表面织构加工激光参数精确选择提供了理论依据。

皮秒激光不同图案化处理氧化锆陶瓷对其粘接性能的影响

目的:研究皮秒激光在牙科氧化锆表面不同图案化扫描处理的结果,以及对氧化锆表面粘接性能的影响。方法:选取160例烧结氧化锆陶瓷试件,随机分为8个研究组,分别为空白对照组(A组)、喷砂对照组(B组)、皮秒激光处理组(C-H组,分别为:皮秒激光蜂窝状扫描、喷砂后皮秒激光蜂窝状扫描、皮秒激光横线状扫描、喷砂后皮秒激光横线状扫描、皮秒激光井字格状扫描、喷砂后皮秒激光井字格状扫描)。扫描电镜观察表面微观组织形貌;激光共聚焦显微镜观察3D形貌,原子力显微镜测量表面粗糙度Ra;X射线衍射仪观测表面晶相组成的转变;电子万能试验机测量抗弯强度,测定氧化锆陶瓷与自粘型树脂水门汀的剪切强度;光学体式显微镜下观察断裂模式;采用SPSS26.0对所得结果进行单因素方差分析及多重检验。结果:皮秒激光在氧化锆表面扫描后,可分别得到蜂窝状、平行的等间距横线状及等间距井字格状图案;不同图案化处理后氧化锆表面粗糙度不同,横线状B组最大,为14.92μm;激光表面处理不会导致表面晶相转变;经过皮秒激光处理后,剪切粘接强度明显增加(P<0.05),C组的粘接强度最大,为(26.86±1.53)MPa,约为A组的7.4倍;断裂模式由A组与B组的完全粘结破坏转变为内聚破坏和混合破坏;激光处理后的氧化锆陶瓷抗弯强度满足临床应用要求。结论:皮秒激光对氧化锆表面进行图案化处理能够提高氧化锆与树脂水门汀的粘接强度,是一种有前景的氧化锆表面改性方法。

755nm皮秒激光联合纳晶微针导入氨甲环酸治疗黄褐斑的疗效观察

目的观察755nm皮秒激光联合纳晶微针导入氨甲环酸治疗黄褐斑的疗效临床疗效。方法将40例黄褐斑患者随机分为两组,试验组采用755nm皮秒激光联合纳晶微针导入氨甲环酸治疗,对照组采用单纯皮秒激光治疗,两组患者治疗前、治疗第2个月、第4个月、第7个月拍照存档,按照黄褐斑皮损面积和严重度指数(melasma area and severity index,MASI)进行评分。结果试验组和对照组从开始治疗的第二个月MASI值就开始出现下降,试验组治疗后第七个月MSAI分值最低,从治疗前(14.86±3.33)下降至(8.33±2.39),对照组的MASI分值下降至(10.23±2.84).试验组分值明显低于对照组(P<0.05)。试验组治疗后MASI下降率为(44.82±5.73)%,明显高于对照组,差异具有统计学意义。结论755nm皮秒激光联合纳晶微针导入氨甲环酸能有效治疗黄褐斑,安全性好,不良反应少。

超皮秒激光联合透明质酸注射在面部年轻化治疗中的应用

目的:探讨超皮秒激光联合透明质酸注射进行面部年轻化治疗的效果。方法:选择2021年1月-2022年6月在笔者医院要求进行面部年轻化治疗的就医者99例,按随机数字表法分为A组(n=33,单纯透明质酸治疗)、B组(n=33,单纯超皮秒激光治疗)、C组(n=33,超皮秒激光联合透明质酸治疗)。评价疗效,对比皮肤生理指标、皮肤屏障功能、不良反应。结果:治疗后,C组总有效率90.91%高于A组(69.70%)及B组(66.67%)(均P<0.05)。C组VISIA皮肤图像分析仪各项指标、经皮水分散失(Trans epidermal water loss,TEWL)、角质层含水量、表皮皮脂含量均较治疗前改善(P<0.05),且治疗后C组各指标改善均优于A组、B组(P<0.05)。三组不良反应总发生率差异均无统计学意义(P>0.05)。结论:超皮秒激光联合透明质酸注射用于面部年轻化疗效肯定,可改善皮肤生理指标、皮肤屏障功能,且未增加不良反应。

超宽调谐(2.6~5μm)中红外皮秒脉冲激光的研究

在超快脉冲激光中,超宽调谐通常应用于超连续谱产生、光谱分析和调制等多个领域。文章利用皮秒脉冲同步泵浦技术,搭建了一种基于MgO:PPLN晶体的“Z”形光参量振荡器,通过具有扇形周期极化的晶体在中红外波段产生了高功率、波长超宽调谐(2.6~5μm)的皮秒脉冲激光源输出。该振荡器由五镜一晶体组成,这五镜片的选择和精确调整是提高光参量振荡器输出性能的关键因素,采用波长为1.064μm的Nd:YVO_(4)皮秒脉冲激光源,选择周期在26~32μm可调谐的MgO:PPLN晶体,最大泵浦功率为15W时,2.66μm、3.44μm和4.99μm处获得了最大输出功率分别为3.41W、2.78W和0.52W的闲频光,相应的光-光转换效率分别为58%、55%、15%,测量到中红外光谱谱宽为2.37nm(2615nm)、Δλ=1.87nm(3687nm)、Δλ=1.30nm(4992nm),观察到在没有任何窄化光学元件条件下长脉冲随波长光谱谱宽具有线性变窄的过程。在2.6~4.5μm波段的激光输出功率均大于1W,实现了高功率,波长超宽调谐的中红外皮秒激光的连续输出。窄谱宽超宽调谐中红外皮秒脉冲激光为超快过程研究和应用领域提供了一种强大的工具。通过优化波长调谐范围和脉冲宽度能够满足不同领域对中红外激光的高要求,对推动相关领域的研究和发展至关重要。

超皮秒激光与CO_(2)点阵激光治疗萎缩性痤疮瘢痕的疗效和安全性对照研究

目的观察并比较超皮秒激光与CO_(2)点阵激光治疗萎缩性痤疮瘢痕的疗效和安全性。方法选择面部萎缩性痤疮瘢痕患者20例,随机选择一侧使用超皮秒激光治疗(试验组),另一侧使用CO_(2)点阵激光治疗(对照组),一共治疗3次,每次间隔一个半月到2个月。治疗前后采用ECCA评分及IGA评价进行疗效评估。调查患者满意度并记录患者在治疗中疼痛程度及不良反应。结果治疗后试验组ECCA权重评分相较于对照组高,P<0.05。试验组与对照组IGA评价瘢痕改善总有效率分别为65%和85%,差异无统计学意义P>0.05。患者对试验组整体满意度为75%,对照组满意度90%。试验组疼痛程度较对照组更低,P<0.05。试验组不良反应较对照组不良反应更少,持续时间更短,安全性更高。结论两种激光均能有效改善萎缩性痤疮瘢痕,但CO_(2)点阵激光治疗的疗效更好;超皮秒激光治疗的疼痛程度及不良反应最少,安全性更高。